Molding machines for producing molds are well known in the art. There is a type of molding machine which introduces molding sand to a molding flask, which generally comprises a pair of an upper and a lower flask, through the sidewall of the molding flask in a horizontal direction (see Patent Document 1). This type of molding machine is superior to another type of molding machine, which introduces molding sand from the top of the molding flask, in the way that the machine which introduces molding sand through the sidewall of the molding flask allows the elimination of a step to turn around the molding flask after the steps of introducing and squeezing the molding sand.
However, in the case of the molding machine which introduces molding sand through the sidewall of the molding flask in a horizontal direction, the molding sand stored in a sand tank descends along the direction of gravity, and then its direction turns by 90 degrees, to the horizontal direction. In this process, a stagnant part of the molding sand may be formed in the sand tank due to the change in the direction the sand flows. After a certain period of molding operations, the stagnant part of the molding sand may cause a formation of a bridge in the sand tank as illustrated in FIG. 5. When the bridge is formed in the sand tank, the operation of the molding machine will be interrupted due to the need for cleaning the inside of the sand tank 202. The letter “S” in FIGS. 5 and 6 denotes the molding sand.
Even when a bridge is not formed in the sand tank, if the rate of introducing the molding sand to the pair of the upper and the lower flask are not equal, the descending rate of the level of the sand in the sand tank would become uneven. As the result, an air channel would be formed in the sand tank, as illustrated in FIG. 6.
Patent Document 2 discloses a so called Top-Under Blowing molding machine, which has air-inlet nozzles in addition to valves at the horizontal and bent parts of upper and lower blowing-heads for introducing molding sand into the molding flask.